1. Field of the Invention
The present invention relates to a printing apparatus such as a printer.
2. Description of the Related Art
Heretofore, a configuration wherein a sheet is conveyed while being held between a conveying roller that rotates under driving from a motor and a pinch roller (a passively driven roller) has been typical for printing apparatus, and several proposals have been made for detailed configurations thereof. For example, as disclosed in Japanese Patent Laid-Open No. H06-135590 (1994), an urging mechanism is provided wherein the center in the widthwise direction of a pinch roller is supported by a supporter, and the supporter urges the pinch roller towards the conveying roller at the widthwise center of the pinch roller. In so doing, pressing force of the pinch roller onto the conveying roller is made uniform, and the effects of pressure force variations due to age deformation of the support mechanism can be suppressed.
In the case of modifying the printing apparatus disclosed in the above literature to a printing apparatus in which the compatible print sheet width has been changed (for example, in the case of modifying an A3 compatible apparatus to a Super A3 or 14″×17″ compatible apparatus), passive roller sets consisting of two pinch rollers and one pinch roller axle are increased or decreased with respect to a conveying reference in the widthwise direction of the print sheet. At this point, there is no problem if the increase or decrease in the width of the corresponding print sheet is equivalent to an even number of pinch rollers from the conveying reference of the print sheet, but if equivalent to an odd number, pinch rollers are added unnecessarily, which inflates cost and increase apparatus size.
Also, while disposing an even number of small pinch rollers at the ends does not affect the apparatus size, higher costs are unavoidable due to the necessity of two types of pinch rollers. Furthermore, if it is attempted to modify and redesign the pinch roller such that an even number of pinch rollers fits in the corresponding print sheet width, it becomes difficult to suitably press the lateral edges of various fixed sizes of print sheets with pinch rollers of the same size.
In contrast, if the pinch rollers are not increased, the lateral edges of wide print sheets are not pressed by the pinch rollers, and in cases such as when the lateral edges of a print sheet curl back towards the print head, the sheet rubs against the carriage mounting the print head, causing ink smudges on its surface. In severe cases this can even cause jams.